Survival of Steinernema feltiae in different formulation substrates: improved longevity in a mixture of gel and vermiculite

Authors: LEITE, LUIS - Instituto Biologicio - Brazil; Shapiro Ilan, David; HAZIR, SELCUK - Adnan Mederes University

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2018
Publication Date: 10/15/2018
Citation: Leite, L., Shapiro Ilan, D.I., Hazir, S. 2018. Survival of Steinernema feltiae in different formulation substrates: improved longevity in a mixture of gel and vermiculite. Biological Control. 126:192-197.

Interpretive Summary: Entomopathogenic nematodes, also called beneficial nematodes, are small round worms that are used as natural bio-pesticides. The nematodes kill insect pests with the help of symbiotic bacteria that the nematodes carry in their gut (and release once they are inside the insect). Beneficial nematodes are already commercially available, but their usefulness and efficacy can be improved if we can develop better formulations that enhance nematode longevity. Therefore, we tested a variety of formulation for their ability to preserve the nematodes. Substrates included vermiculite, polyacrylamide gel, diatomaceous earth, potting mix, peat and water (as a control). We discovered that a combination of vermiculite and polyacrylamide gel was the best substrate. This new formulation may be used by researchers and commercial nematode producers to improve beneficial nematode survival and performance in insect pest suppression.

Technical Abstract: Entomopathogenic nematodes (genera Steinernema and Heterorhabditis) have a symbiotic association with bacteria, which make them highly virulent to insects. These nematodes have been commercially produced as biopesticides, but nematode products still face significant barriers related to the preservation and formulation. This study aimed to assess the performance of seven different formulation substrates and two combinations involving vermiculite and gel, to preserve Steinernema feltiae at three temperatures: 15°C, 25°C and 35°C. Three experiments were established. The first and second assessed the survival and mobility of S. feltiae infective juveniles (IJs) in 7 different substrates: mushroom compost (Hobin Wood Landscaping Products), peat (sphagnum peat moss), Potting mix (Metro Mix®), polyacrylamide gel, diatomaceous earth, vermiculite, and water (control). The third experiment assessed the survival of IJs in combinations of the two best substrates selected from the prior tests: vermiculite and polyacrylamide gel. These substrates were tested separately and combined, resulting in six treatments: vermiculite, polyacrylamide gel (1.33%), double polyacrylamide gel (2.66%), vermiculite + gel (1.33%), and vermiculite + double gel (2.66%), and water (control). The performance of the formulations varied according to temperature. The greatest IJs fitness at 35°C and 25°C was observed in peat and vermiculite, respectively, and at 15°C the gel and water treatments were superior. In general, vermiculite and polyacrylamide gel were the two best substrates considering that they provided the best results at 25°C and 15°C. The polyacrylamide gel formulation held higher numbers of nematodes in the substrate compared with the solid substrates. The mixture of vermiculite + double polyacrylamide gel provided the best preservation at 35°C compared to the substrates tested separated. The present study is the first to develop a formulation combining vermiculite with polyacrylamide gel, which preserves S. feltiae IJs with viability higher than 80% for at least 30 days at 35°C, 233 days at 25°C, and 241 days at 15°C.